


Kirk/Spock Parasitic Twin Soulmate AU

by BaronVonChop



Category: Star Trek: Alternate Original Series (Movies), Star Trek: The Original Series
Genre: Alternate Universe - Soulmates, Fluff, M/M, Parasitic Twin Soulmate AU, Soulmate-Identifying Marks, Soulmates, mild body horror, parasitic twins
Language: English
Status: Completed
Published: 2019-06-01
Updated: 2019-06-01
Packaged: 2020-04-06 05:03:33
Rating: Teen And Up Audiences
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 960
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/19055776
Author URL: https://archiveofourown.org/users/BaronVonChop/pseuds/BaronVonChop
Summary: A Star Trek Kirk/Spock AU where everybody in the world is born carrying their soulmate’s parasitic twin. Mild body horror, but mostly odd fluff.





	Kirk/Spock Parasitic Twin Soulmate AU

**Author's Note:**

> Thanks to [zjofierose](https://archiveofourown.org/users/zjofierose) for beta reading! Any remaining mistakes are my own.
> 
> For the basics of a parasitic twin AU, please see:  
> <https://baronvonchop.tumblr.com/post/182334942888/soulmate-au-where-everyone-has-a-parasitic-twin>

When the kids in his class attend a special assembly about soulmates, James T. Kirk learns that it is not uncommon for humans to have nonhuman soulmates. He is therefore not overly concerned about the Vulcan parasitic twin he carries on his left side. Everyone has a soulmate, and his just happens to be Vulcan.

As he grows up, he sometimes sits and looks at the pale skin and greenish veins and wonders what his soulmate is like. The three little stubs of fingers poking out of the PT’s mass do not offer much of a clue.

He knows he has a soulmate, but the universe is full of people of many shapes and genders, and, more importantly, so is Starfleet Academy. So why not explore a bit in the meantime? This whole soulmate thing will work itself out.

* * *

When Sarek and Amanda have explained the concept of soulmates to Spock, he sits looking at the lump of pink flesh on his stomach, at the shape of a sole of a foot on its surface.

Most Vulcans have Vulcan soulmates, Sarek said, and it shows them with whom they will eventually share the ritual of _pon farr_. Amanda said that, with humans, things are a little different. The human version sounds less logical.

His parents are unsure which version he will experience.

Curious.

Spock puts it out of his mind. It will happen when it happens.

* * *

The moment Kirk meets his new first officer, he is sure. He has met other Vulcans before, but there is something about Spock that makes Kirk feels like he has known him all his life. In a way, he has, as Kirk has always had a piece of Spock with him.

Perhaps that is why he teases Spock. Not that Spock is difficult to tease: everything with him is logic, logic, logic. And surely Spock, with his keen and analytical mind, must realize that Kirk is his soulmate. Surely the teasing cannot bother him.

* * *

Spock has no idea why his captain insists on carrying on in that manner. It is unprofessional, undignified, and, above all, illogical.

* * *

It takes a while, but slowly doubt starts to emerge in Kirk’s mind. Could he have been wrong? Could his soulmate be a different Vulcan? If that is true, then he has been taunting an innocent person.

When he asks the ship’s doctor about it, McCoy shrugs. For all the things modern tricorders can do, they cannot shine any light on soulmates. Parasitic twins may look like a part of another person’s body, but every scan known to science only returns the DNA, tachyon signature, etc, of the host.

McCoy has medical records of the members of the crew. Can he verify whether the fingers on Kirk’s PT resemble Spock’s? But the old country doctor smiles and shakes his head. That would be telling.

Kirk starts observing Spock’s hands when he can, trying to see if his fingers resemble the ones on Kirk’s PT. He thinks they do… probably.

* * *

Dr. McCoy keeps trying to bring up the topic of PTs with Spock. Did someone put him up to it? It is hardly an appropriate topic of conversation, even for a doctor.

Spock keeps his answers short: his PT has not been bothering him unduly. It twitches or flexes occasionally, but it does not interfere with his ability to perform his duties.

If that will be all, he should return to his post.

* * *

Sulu and Chekov are worried about him, Kirk can tell. He sees them exchange glances from time to time.

His crew needs him to focus. Still, it can be hard to ignore the frantic wiggling of his PT’s fingers during tense moments. It is especially distracting when Kirk himself is in danger, which is when the movements seem especially frantic.

And yet Spock looks barely fazed. It can’t be Spock.

Why couldn’t it be Spock?

He wishes it were Spock. He wishes that, when he feels the fingers on his left side tense up, he could look over to see Spock looking back at him, worrying about him.

He worries about Spock anyway.

* * *

The captain is looking increasingly agitated lately.

Spock has been gathering evidence and formulating possible tests. As he watches the captain shift and fidget in his chair, Spock turns to his station. Once he is sure nobody is watching, he touches his PT, gently massaging the little foot there. Slowly, gradually, the captain starts to relax.

Ah.

* * *

Now that Kirk has decided that it can’t possibly be Spock, he finds himself appreciating Spock all the more. Spock is not only a genius, he is dependable and surprisingly kind, in his own way. Even his endless references to logic is starting to seem endearing instead of aggregating.

Whoever has Spock for a soulmate is very lucky.

* * *

Spock really must say something to Kirk, but he hesitates. Having gotten this far, he is unsure how to break the news to Kirk.

Uhura suggests that the human custom of birthdays may offer the perfect opportunity, since Kirk’s is coming up. When Uhura tells him about birthday cards, he knows that is just the way to do it.

Uhura recommends putting simply, “From your soulmate,” and handing it to him. She says it is romantic, and from the way she says it, that is a good thing.

It strikes Spock as somewhat vague. He decides to add on, “It is I.”

The blissful look of realization on Kirk’s face as he reads the card proves that Spock’s approach was correct.

“But I was sure… How did you ever...?” As soon as the question is out of his mouth, he realizes he has given Spock the perfect opportunity. “Oh no. Please don’t say it.”

Spock raises an eyebrow.


End file.
